Conventionally, electronic devices include one or more printed circuit (pc) boards for electrically connecting components, e.g., resistors, capacitors, etc. As electronic devices have become more complex, the component interconnections on printed circuit boards have necessarily also become more complex. As a result, to prevent the overcrowding of components and interconnections on the pc boards, many complex electronic devices commonly include pc boards having more than one layer on which the interconnections between the components may be constructed.
During the manufacture of a multi-layer pc board, a substrate coated with a conductive metal, i.e., a pc board layer, is covered with a film to mark the areas which are to remain metallized, i.e., the interconnections. The layer is then lowered into an acid bath to remove the conductive metal from the areas of the layers left uncovered by the film. After the selective removal of the metallization from the layer, the layer is aligned and stacked, along with other layers of the multi-layer pc board, subsequent to which the layers are pressed together by lamination equipment to form the multi-layer pc board. During the pressing process, however, the layers sometimes float out of alignment, resulting in incomplete component interconnections. This misalignment often remains undetected until after the components are reflowably soldered onto the multi-layer pc board, in which case the completed pc board may operate incorrectly, if at all. As a result, the pc board must be analyzed to determine the source of the incorrect operation, thus wasting time and material.
A further source of error during the pc board manufacturing stage resides in the stacking of the layers, which is typically performed manually. During this process, the possibility exists that the layers could be stacked incorrectly. The incorrect stacking of outer layers, which are usually etched with a known circuit pattern, is easily detected. The incorrect stacking of inner layers, however, is very difficult to detect. Therefore, as in the case of misalignment, the error may not be discovered until after the pc board is completed, thereby resulting in wasted time and material, both of which may be reflected in an increased product cost.
Thus, what is needed is a multi-layer pc board which may be visually inspected, prior to component placement, to verify proper assembly and alignment of the layers. Furthermore, a method for constructing such a multi-layer pc board is also needed.